1. Field of the Invention
The present invention relates to a method of manufacturing ink jet heads.
2. Description of the Related Art
An ink jet head with a basic structure includes an actuator that extends in its longitudinal direction when applied with an electrical signal, and a diaphragm attached to one end of the actuator and defining an ink chamber filled with ink. When the actuator extends in its longitudinal direction, the actuator deforms diaphragm into the ink chamber, thereby pressurizing the ink in the ink chamber. This ejects an ink droplet from a nozzle formed in a nozzle plate opposite the diaphragm. An ink jet head of multi-nozzle structure is formed with a plurality of single-nozzle units with their nozzles aligned.
Techniques such as super fine machining and super precise intimate contacting and bonding are introduced into manufacturing methods of the heads to manufacture the heads in a compact size and with a high-density nozzle arrangement. It is important that each nozzle in the head is capable of ejecting ink droplets having the same weight and at the same speed. To this end, the dimension or each nozzle unit and the thickness of the bonding layer used in assembling the nozzle unit must be as uniform as possible to minimize the variation in weight and in ejecting speed of ink droplets.
The bonding technique used for bonding the actuator and the diaphragm is particularly important, because bonding variation is closely correlated with the speed of ink droplets and the amount of ink ejected from the nozzle. Specifically, initial pressure imparted on the diaphragm will vary depending on the thickness of the bonding layer. Accordingly, the stress on the diaphragm, and consequently the deform amount of the diaphragm, will also vary depending on variation in the thickness of the bonding layer. Even if actuators attached to different diaphragms are displaced by the same amounts the same ink droplet ejection capability will not be attained if there is variation in the deform amount of the diaphragms.
Small size heads with high density nozzle arrangements include a greater number of smaller size actuators. Therefore, not only does the end face of the actuator where adhesive agent is coated have a small area, but the number of bonding portions also increases. This makes it difficult to have the same bonding thickness in all the bonding portions within the head. Furthermore, because adjacent actuators are separated by only a vary short distance, the adhesive agent is likely to bridge over and connect the two adjacent actuators during the bonding process. Once the adhesive agent connects the two adjacent actuators, the behavior of one actuator will be transmitted to the other actuator, resulting in interference between the actuators, so the ink ejection performance is degraded.